The rapid development in data and telecommunication creates a constant flow of new possibilities to serve a number of new needs and to meet new demands. The time when each network offered one single standard service is gone. It is now possible to offer a plurality of services having different characteristics in the same network in order to serve individual, specific needs. An individual household will be able to select their own set of services according to their own demands among a multitude of possibilities. Housing companies can rationalise administration and maintenance of their buildings and at the same time offer new types of services to their tenants. Other companies and also communities can benefit from the offered possibilities.
One of the techniques which then is used is virtual local networks, or techniques within the wider area virtual broad cast domains. The term virtual local networks is some time given the acronym VLAN (Virtual Local Area Network). The acronym itself VLAN is a market term which is used by almost every switch manufacturer, but it lacks a detailed definition. This results in that different manufacturers can use the same term without their equipment being compatible. A definition which is broad enough to cover different manufacturers equipment is as follows. VLAN: A logic level two (link level) broadcast domain. The selection from the total broadcast domain, i.e. all ports and MAC addresses (Medium Access Control), can be made in any of the following ways. a) Select the group of ports, b) Select a group of MAC addresses or c) Select a group of protocols, for example IP or IPX.
The standard IEEE 802.1Q, which has been adapted as industrial standard for VLAN, is based on standard LAN switches according to IEEE 802.2 standards. Switches which implement the standard IEEE 802.1Q are in principle switches compatible with the standard IEEE 802.1D (LAN switches), which have modifications for rules relating to incoming and transmitted data packets, an additional protocol for identifying VLAN capability of other switches and connected end systems and in addition having an VLAN transport mechanism based on implementation of VLAN marking of data packets via specific identification bits in the data packets.
The standard IEEE 802.1D describes how a so called LAN-switch should operate. A LAN-switch is to communicate user data in layer two in the OSI model, based on MAC addressing. Within this standard there are rules relating to transmission logic and how ports shall act in order to comply with for example requirements on transparent bridging, i.e. that the transmission logic remains invisible for apparatuses connected to the domain. Within the standard there are also topology rules in order to avoid loops.
In order to offer Ethernet traffic priority there is the standard IEEE 802.1p. This is an addition to the standard IEEE 802.1D. Ethernet communication is performed using data packets, to which a packet having an address is added. The communication is also divided into different levels, where each level has its own address packets.
The technique for virtual local networks is used to reduce costs associated with addition, moving or change of end user equipment within, for example, companies. The personnel within a part of the company, for example the purchasing department, shares the same resources in the network. By means of associating all users and resources to a VLAN it is possible to add new or remove old equipments, move personnel between floors and change their department belonging without moving cables or change access filters in IP-path selectors.
In the American Patent U.S. Pat. No. 5,751,967 a system for configuring virtual local networks is described. The system sets the switches of the network in a desired manner so that connected end stations are connected in a desired topology and the system can reconfigure the switches when the end stations move. The system has a central device for carrying out these tasks. This device comprises a circuit for sensing modifications of the topology. The central device also has a circuit containing rules how the switches are to be reconfigured when end stations are moved and a circuit for reading the rules and determining how end stations and switch ports are to be grouped. Finally, in the central device a circuit is incorporated which carries out the automatically decided reconfiguration. The system is efficient but has the drawback that it is completely automatically controlled by the central device and can not in any way easily be operated by the users.
The International Patent Application WO98/44684 describes a technique for creating virtual broadcast domains, which are virtual networks within a larger physical network. Also, a log in method is described according to which a terminal being switched on is associated with a first virtual broadcast domain. When the user later logs on he is switched to the virtual broadcast domain to which he belongs. A part of the stations in the larger network are connected to this virtual broadcast domain. A message from one of this stations only reaches the stations connected to the domain. The log in method has the advantage that it is possible to log on from an arbitrary terminal, but it also brings about administrative costs.